"High-cap mags hold more bullets than standard magazines." — In-game description
The High-Capacity Mag is a weapon attachment featured in Tom Clancy's Rainbow Six: Vegas. It increases a weapon's magazine size by 20%. High-Capacity Mag can only be equipped onto pistols though. Since pistols have unlimited reserve ammunition in the series, the High-Capacity Mag attachment is really only useful if a player finds themselves running out of pistol ammunition often in a firefight. High-Capacity Mag cannot be equipped onto the Raging Bull or Glock 18.